A high resolution imaging system with compact size, light weight, high speed, low power consumption, and low cost is in high demand. Resolution can be defined in many ways. In this disclosure, image resolution means spatial image resolution which is defined as the number of picture elements used to represent an image captured with a given field of view and depends on mainly image sensor resolution. Image sensor resolution is determined by various factors including the size of the image sensor and the pixel size of the image sensor. To provide high image sensor resolution for a given pixel size, the size of the image sensor needs to be increased, which causes the aperture and the focal length of an imaging system to be increased. Such an imaging system tends to become bulky and heavy as well as cost more. To increase image sensor resolution for a given size of the image sensor, the pixel density needs to be increased by reducing the pixel size. Smaller pixel, however, has less sensitivity. Increasing image sensor resolution can cause other problems including more processing time, more power consumption, and higher cost. Advantages using a low resolution image sensor in the imaging system include low cost, low volume, low power consumption, and possibly high sensitivity by increasing the pixel size for a given size of the image sensor. There are a few approaches to increase image resolution without increasing image sensor resolution. They are categorized as either mosaic or super resolution approaches.
In the mosaic method, a plurality of magnified sectional images of an object obtained from a lower resolution image sensor is stitched by an image processor to generate a single higher resolution composite image of the object. U.S. Pat. No. 6,710,801 to Kubo discloses an image taking and processing device comprising an image taking lens having zoom functionality. The system of Kubo improves image resolution only for central area.
U.S. Pat. No. 4,383,170 to Takagi discloses an image input device comprising image dividing means including shutter means and an compound eye lens to generate partial images of an object. The device yields complicated structures while providing a fixed resolution unless shutter means and the compound eye lens are replaced.
U.S. Pat. No. 6,639,625 to Ishida discloses an image sensing device comprising a movable image sensing optical unit having first and second focal lengths. The direction control unit of Ishida moves a whole housing containing an optical unit and an image sensor, resulting in a complicated driving mechanism.
In the super resolution method, a plurality of low resolution images with subpixel relative displacements is fused to generate a single higher resolution image. Various data fusion algorithms are introduced by M. Elad and A. Feuer, “Restoration of a Single Superresolution Image from Several Blurred, Noisy, and Undersampled Measured Images,” IEEE Transactions on image processing, Vol. 6, No. 12, December 1997.
U.S. Pat. No. 6,686,956 to Prakash discloses an increased resolution imaging device comprising an optical wedge assembly to obtain multiple images using the super resolution method. The improvement of resolution is limited by the shape of the optical wedge. Also, the actuator moving the wedge assembly uses a macroscopic servo mechanism which can induce vibration and time delay causing deterioration of the image quality.
U.S. Pat. No. 7,003,177 to Mendlovic discloses an image sensing device comprising a periodically patterned mask and a motion generator generating multiple fields of view, related to one another by sub-pixel shifts. The system of Mendlovic does not include details how to generate multiple fields of view.
Both mosaic and super resolution methods require the change of an optical axis. Those methods can be used effectively to produce high resolution images in real-time when the optical axis of an imaging system is changed in high precision, high speed, and large range. Also, the optical axis change of the imaging system facilitates advanced features such as providing true panoramic images. In conventional digital cameras, a panoramic image is provided by simply cropping the top and bottom portion of a captured image, while actual panoramic cameras have complicated structures including rotating or swing lens to provide a wide angle of view. The imaging system having a variable optical axis enables a wide angle of view to produce true panoramic images without increasing complexity and cost.
Conventional imaging system does not provide optical axis change unless it adds bulky structure and cost. To provide a high image resolution, compact size, light weight, high speed, low power consumption, and low cost imaging system, the imaging system having the capability of fast and precise optical axis change is provided.